Cognitive performance, creativity and stress levels of neurotypical young adults under different white noise levels

Noise is often considered a distractor; however recent studies suggest that sub-attentive individuals or individuals diagnosed with attention deficit hyperactivity disorder can benefit from white noise to enhance their cognitive performance. Research regarding the effect of white noise on neurotypical adults presents mixed results, thus the implications of white noise on the neurotypical population remain unclear. Thus, this study investigates the effect of 2 white noise conditions, white noise level at 45 dB and white noise level at 65 dB, on the cognitive performance, creativity, and stress levels of neurotypical young adults in a private office space. These conditions are compared to a baseline condition where participants are exposed to the office ambient noise. Our findings showed that the white noise level at 45 dB resulted in better cognitive performance in terms of sustained attention, accuracy, and speed of performance as well as enhanced creativity and lower stress levels. On the other hand, the 65 dB white noise condition led to improved working memory but higher stress levels, which leads to the conclusion that different tasks might require different noise levels for optimal performance. These results lay the foundation for the integration of white noise into office workspaces as a tool to enhance office workers’ performance.

www.nature.com/scientificreports/ with ADHD, while a limited number of studies, as elaborated below, have investigated the effect of exposure to white noise on the cognitive performance of neurotypical adults. Although the MBA model suggests that healthy individuals with proper internal neural noise do not necessarily require white noise to optimize their cognitive performance 6 , recent works suggest otherwise. For example, a study conducted on neurotypical individuals showed that those who are frequently exposed to white noise present improved cognitive performance 3 . Furthermore, Othman et al. 4 concluded that low intensity white noise enhanced the auditory working memory performance of 20 healthy adults. Finally, Angwin et al. 9 found that participants who were exposed to white noise showed higher attentional capacity, enhanced lexical acquisition and improved recall accuracy compared to a non-noise condition. Given the potential of white noise in boosting cognitive functions, the primary aim of this study is to investigate the effect of different white noise levels on the cognitive performance of neurotypical adults in office spaces. We focus on workers associated with office and administrative work as they represent a major part of the general workforce around the world and specifically in the U.S 14 . Office work is often associated with knowledge-based work 15 . Such work flourishes in workspace environments that promote optimal conditions for better cognitive capabilities (e.g., learning, thinking, reasoning, remembering, attention, perception and executive function [16][17][18] Additionally, cognitive skills are a necessity to overcome work-related challenges and create high-quality work. Moreover, employees' creativity has always been the most important asset for the success of businesses, as it is essential for organizational growth and development 19 . Hillier et al. 20 suggest that high level of white noise leads to increased stress levels which results in deteriorated creativity. Similarly, Martindale and Greenough 21 concluded that a 75 dB white noise can cause a decrease in creative thinking among people. However, Toplyn and Maguire 22 found contradicting results. After assessing their creativity levels using the Remote Associate Test (RAT), participants were asked to complete other creativity-related tasks under three conditions: low, moderate, and high white noise. Their results suggest that highly creative participants, scoring high on the RAT test, demonstrated the highest creative tendencies when exposed to moderate white noise levels. In summary, there have been a few studies that investigated how white noise influences creativity with mixed results. In fact, in their review, Mehta et al. 23 concluded that white noise is generally associated with reduced creativity levels, but pointed out that more research is needed. Thus, a secondary aim of this study is to determine how different white noise levels affect the performance of neurotypical office workers' creativity.
Finally, studies have shown that exposure to high levels of white noise can lead to stressful reactions manifested by physiological arousal. In their study, Nakajima et al. 24 used white noise (70 dB) as an auditory-stress inducing mechanism while studying how music can help individuals recover from a stressful situation. Their results suggest that white noise was associated with an increase in heart rate. Stress responses have also been demonstrated in other studies when participants were introduced to white noise between 75 and 93dB 25 and at 90 dB 26 . In the latter study, when exposed to 90 dB for 15 min participants demonstrated a significant increase in the secretion of salivary chromogranin A, a protein used as an indicator of stress. Most of the related literature has focused on relatively high levels of white noise, which is why a tertiary aim of this study is to determine the effect of different white noise levels on the physiological responses and stress levels of neurotypical office workers.
In this study, we assess the effect of two white noise conditions, white noise at 45 dB and white noise level at 65 dB, on the cognitive performance, creativity, and physiological responses of neurotypical adults in a private office space. Among the different cognitive functions, we focus on sustained attention, selective attention, inhibition, working memory as well as speed and accuracy in completing tasks as these functions are crucial to the success of the daily office tasks. Electrodermal activity (EDA) is used to assess participants' physiological responses. The two-white noise conditions are compared to a baseline condition where participants are exposed to ambient noise in the office. The paper is organized as follows: "Methodology"section outlines our methodology; "Results"section introduces the results; "Discussion"section provides discussions and analysis. Finally, "Conclusions"section is a summary of our conclusions.

Methodology
Participants. Forty adults participated in this study voluntarily. A power analysis was conducted using G*Power version 3.1.9.7 to determine the sample size 27 . For an effect size (f = 0.2) and an α error probability = 0.05, the obtained sample was sufficient for a power of 80%. Of the 40 participants, 24 identified themselves as male and 16 as female. The average age of the participants was 25.82 ± 7.53. Also, 37 specified that they consider their right hand as the dominant one, and the remaining 3 indicated that their left hand is dominant. All 40 participants were graduate students at the University of Southern California. The study was limited to participants between 18 and 64 years old. Individuals with visual problems, hearing deficits, noise sensitivity, and/ or physical injuries, making it uncomfortable to sit for a long period, were not eligible to participate. A screening survey was used for determining eligibility. If a participant felt uncomfortable during the experiment, they were given the option to discontinue at any point. Every participant performed an online hearing screening 28 to ensure they had normal hearing sensitivity in both ears. This test consists of three main parts: (1) four selfevaluation questions about hearing abilities, (2) tone testing at 500, 1000, and 4000 Hz, and (3) conversation comprehension where participants would listen to a short conversation and respond to related questions 28 . At the end of the test, participants would be provided with a hearing report stating their hearing loss level. Only participants with no hearing loss were eligible to be part of the experiment. One participant was excluded from the analysis due to unrealistically fast response speed on survey responses; data from the remaining 39 participants were included in all analyses. The study was approved by the Institutional Review Board of the University of Southern California (UP-20-00389 IRB study number). All participants reviewed the informed consent and agreed to participate in the experiment. All experiments were performed in accordance with relevant guidelines and regulations. www.nature.com/scientificreports/ Auditory conditions. The experiment consisted of three auditory conditions: white noise at 45 dB, white noise at 65 dB, and ambient noise. According to the Center for Disease Control and Prevention (CDC), people exposed to a 70 dB noise level for a prolonged time might feel overwhelmed and annoyed 29 . To eliminate this effect on our experimental results, we chose a 65 dB as the high white noise condition. On the other hand, the U.S. Environmental Protection Agency (EPA) recommends a 45 dB for indoor activities which is why a 45 dB was chosen our low white noise condition 30 . White noise was presented via Bose QuietComfort 35 headphones with active noise cancellation to reduce background noise. The white noise was generated using Audacity software version 3.0.2; this software has been used previously by several research studies to generate white noise tracks 4,8,9 . The experiments were conducted using a Lenovo ThinkPad X390 Yoga (Intel Core i7-8565U CPU @ 1.8 GHz equipped with 16 GB RAM) with Realtek Audio drivers (version 6.0.8757.1). The baseline condition was set by asking participants to complete their tasks without wearing the headphones; in this condition, participants were exposed to the ambient noise of the office space. During this condition, the noise level was measured continuously using a BAFX digital sound meter 31  A brief explanation was added before every test to inform the participant of the task's nature and to provide brief instructions for proper completion. It is worth noting that the tests did not have a fixed time, because the progress of the test is response-dependent; as soon as the participant provides a response, the next question is presented immediately. A thorough description of each test follows.

Continuous performance test.
This test measures sustained attention, which is defined as the ability of an individual to focus on a stimulus for a certain period while ignoring distracting stimuli 33 . Previous studies report a moderate reliability level of the continuous performance ranging between 0.4 and 0.7 34 . The test includes 16 different stimuli formed by combinations of four shapes (i.e., star, circle, square, and triangle) and four colors (i.e., yellow, red, white, and blue). During the test, participants were presented with a total of 320 stimuli, each appearing on the screen for 0.3-s followed by a 1-s inter-stimulus (blank screen) period before presenting the next stimulus. Participants were asked to press the "Enter" keystroke whenever they saw the target stimulus: a red star. If a participant failed to react within the 1.3-secs time span when a red star appeared or pressed the "Enter" keystroke when a shape other than the red star was presented, the response was marked as incorrect.
The target stimulus accounted for 30% of the images. Color-conjunctive distractors (red non-star) appeared in 17.5% of the trials, and shape-conjunctive (non-red star) appeared in 17.5% of the trials. The remaining 35% of the trials were non-conjunctive distractors, where the shape and color were different from the target stimulus. The order of appearance of stimuli changed every time the test was run to limit any learning effect across the different auditory conditions.
Stroop test. This test assesses an individual's selective attention and inhibition, that is, the capability to overcome a learned response 35 . The Stroop test is widely accepted as a reliable assessment for inhibition and selection attention. For instance, Siegrist 34 reported a 0.73 reliability for the Stroop test among adults. In this test, participants were presented with 16 different combinations of four-color words in the same four ink colors (i.e., blue, red, yellow, and green). The test consisted of 120 trials, with 50% of the trials showing consistent word and ink color combinations and the remaining 50% presenting color words printed in an inconsistent ink color (e.g., the word "yellow" written in "red" ink). Each word appeared for 1 s followed by 1 s of blank screen before presenting the next word. Participants were required to indicate the ink color, not the color represented by the word itself, with a keystroke of numbers 1 through 4 each associated with a respective color. To help the participants make this association, colored pieces of paper covered each of the number keys according to the color they represent (e.g., a blue piece of paper covered the key for number 1). If a participant failed to react within the 2 s period or pressed the wrong key, the response was marked as incorrect. The order of the trials changed every time the test was run to limit any learning effect across the different auditory conditions.
Two-back test. This test assesses working memory 36 . The test is reported to have a moderate to high reliability level 37 . Participants were presented with a sequence of letters and pressed the "Enter" key when the current letter was the same as the letter presented 2 steps earlier in the sequence. The full sequence was composed of 120 letters, each appearing on the screen for 0.5 s followed by a 1.5 s of blank screen before proceeding to the next letter. If a participant failed to react within the 2 s time span when they should have pressed the "Enter" keystroke or pressed the "Enter" keystroke falsely, the response was marked as incorrect. Out of the 120 trials, 30% were target letters while the remaining 70% were non-target. Participants were presented with a different list of letters in each condition to limit any learning effect.
Remote associate test. This test assesses creativity levels, particularly an individual's ability to make associations 38 . The test has been extensively used and is highly reliable. The Spearman-Brown reliability reported by Mednick was 0.92 39 . Participants were presented with three cue words and were asked to determine a fourth word that links the other three words together (e.g., cottage, Swiss and cake are three cues linked by the word "cheese"). Word selections for this study were acquired from a word bank developed from previously published studies 40  www.nature.com/scientificreports/ answer before moving to the next set of words. Each trial had only one correct answer, and sores were calculated as the number of correct answers out of 10 trials for each auditory condition.
Typing performance test. This test measures an individual's speed and accuracy in preforming computer work 41 . Participants were presented with a printed paragraph and were asked to type the text into a digital format on a computer. Automatic spelling and grammar checks were disabled in the word processing software during the test. Writing speed was measured as the time needed to type the paragraph, and accuracy was measured as the number of errors made. Participants were provided with a different paragraph of similar size (300 words) and difficulty level (elementary level) for each auditory condition. These paragraphs were acquired from a public resource 42 .
Electrodermal activity. EDA is a measure of variation in electrical conductance at the surface of the skin 43 .
EDA is associated with emotional arousal, stress intensity, and increased cognitive workload of individuals 43 , and therefore, is considered a valid physiological indicator of stress 44 . In this study, EDA was monitored continuously using a wrist band sensor (Empatica E4), which applied an unnoticeable yet continuous voltage to the skin surface to measure variation in skin conductance. EDA was measured in microSiemens (μS) with a sampling frequency of 4 Hz (non-customizable) and a range of 0.01-100 μS 45 . EDA analysis was completed using two components 44 : (1) the tonic component which refers to slow variations in the EDA signal over time measured through the tonic component and (2) the phasic component which refers to rapid and smooth transient events noticeable in the EDA signal. The MATLAB Ledalab toolbox was used to analyze the EDA raw data 46 . The software uses the "Continuous Decomposition Analysis" to decompose the raw EDA data into the tonic and phasic components. The full analysis comprises four steps: estimation of the tonic component, nonnegative deconvolution of phasic SC data, segmentation of driver and remainder, and reconstruction of SC data 47 . However, in this study, the analysis is solely focused on the tonic component of the EDA since the experimental procedure did not include any specific stress-inducing events that required identifying sudden changes via EDA's phasic component. The tonic component of the EDA data is computed based on the mathematical process of deconvolution 48 , where only data intervals that do not reflect any phasic activity are used to estimate the tonic component. Significant peaks in the EDA data are detected whenever a local maxima shows a difference of 0.2 μS, in comparison to a preceding and succeeding local minima. These peaks are the indicators of phasic activity. Thus, the tonic component is calculated by averaging the values of the driver function governing the EDA data outside the phasic activity intervals. For more details about the "Continuous Decomposition Analysis", please refer to the following studies: 47,48 The difference in the mean tonic activity between baseline EDA and the EDA during the auditory conditions was calculated for every participant. This difference was compared across the different conditions to determine the effect of noise on the EDA.
Procedure and experimental design. The experiment took place in a private office at a time when no occupants were present in neighboring offices to limit external distractions. The window's blinds were kept shut and the same artificial lighting conditions were maintained for all participants to limit the effect of lighting on participants' performance. Similarly, a 24 °C indoor temperature was set and maintained throughout the experiment. This setup mimics a private office setting with standard lighting and thermal conditions and no distracting noise (e.g., no telephone rings, printer noise, chat, etc.) At the outset, participants indicated their gender, age, and dominant hand, reported any sensitivity to noise and completed the online hearing screening. The E4 45 was placed on the participant's wrist, and the participant remained still for 5 min to collect an EDA baseline. Then, participants completed the 5 tests in the same order under each auditory condition, starting with the continuous performance test, followed by the Stroop test, two-back test, remote associate test, and finally the typing performance test. Participants were exposed to the 45 dB and 65 dB white noise continuously through the headphones while performing the tests. During the ambient noise condition, participants were asked to complete their tests without wearing the headphones. The study follows a within-subject experimental design, where every participant completed all three conditions. The order of the three auditory conditions was randomized for each participant using a Latin square design 49 . The total duration of the experiment was around 2.5 h.

Data analysis.
A repeated-measures analysis of variance (ANOVA) was used to analyze the outcomes under study during the various auditory conditions as a within subjects' factor. In this study, the dependent variables are sustained attention, selective attention, inhibition, working memory, creativity, performance, and stress level. The independent variables are the three noise conditions: white noise at 45 dB, white noise at 65 dB, and ambient noise. Tukey HSD analysis was employed to examine the significant differences in the outcomes between each of the three conditions. A p-value of 0.05 was used to determine statistical significance. The statistical analysis was conducted using the IBM SPSS statistics software, version 27 50 .

Results
Sustained attention: continuous performance test. Sustained  Working memory: two-back test. Significant Table 1.
Additionally, a summary of the post hoc analysis is presented in Table 2.

Discussion
This study examined the effect of white noise levels on cognitive performance, creativity, and stress levels in neurotypical young adults, which is not well studied in the literature. In general, white noise level at 45 dB resulted in better cognitive performance in terms of sustained attention, accuracy, and speed of performance as well as enhanced creativity and lower stress levels. The 65 dB white noise condition led only to improved working memory. Results related to creativity, performance and stress levels are especially important to note because white noise condition at 45 dB resulted in significantly better creativity levels compared to the ambient noise at around the same dB level. This points out to the signal characteristics of white noise at 45 dB supporting creativity and shows that white noise condition at 65 dB neither reduces nor improves creativity compared to ambient noise at 45 dB. In addition, white noise condition at 45 dB resulted in significantly better performance both in terms of accuracy and speed compared to the white noise condition at 65 dB. Moreover, participants had lower levels of stress during white noise condition at 45 dB compared to the white noise condition at 65 dB. Previous studies have shown that white noise results in improved recognition memory 51 , speed of arithmetic computations 52 and lexical acquisition of novel word forms 9 in neurotypical adults. Our results extend these www.nature.com/scientificreports/ findings by showing that white noise at 45 dB and 65 dB enhanced sustained attention and working memory, respectively, in comparison to the ambient noise. Yet, the differences in these two outcomes were not substantial to have major consequences from a practical aspect. Nevertheless, the fact that white noise conditions -not the ambient noise condition-triggered better cognitive performance remain worthy of note. This may be as a result of the white noise sound characteristics (pitch and frequency), which makes it resemble the sound of rain, waves or the wind going through tree leaves 53 , and allows it to be perceived as pleasant to the senses 54 in comparison to the ambient noise. It is worth noting that a general comparison, with the ADHD-related literature, shows that our neurotypical population needed comparatively lower levels of white noise to boost their cognitive performance. For instance, studies examining the effect of white noise on ADHD individuals conducted by Soderlund et al. 55 and Chen et al. 56 used 80 dB and 78 dB, respectively, when studying working memory, while Baijot et al. 57 and Soderlund et al. 58 used 77 dB and 78 dB, respectively, to study attention. The MBA model postulates that individuals with low dopamine levels require high white noise levels to trigger enhanced internal neural activity but demands less white noise when dopamine activity is high 13 . This explains why researchers focusing on ADHD population (characterized by low dopamine circuity) usually use high white noise levels as well as why enhancements in cognitive functions were noted in our neurotypical population at comparatively lower white noise levels.
Previous studies suggest that low to moderate white noise levels can be enough to induce a high construal level leading to better abstract processing thus enhancing creative thinking 23 . On the other hand, the literature also presents a plethora of studies demonstrating that high levels of white noise can impede the creativity of individuals. For instance, Martindale and Greenough 21 concluded that a 75 dB white noise resulted in the lowest scores on the remote associate test in comparison to the control (no white noise) condition. Similarly, results from the study conducted by Hillier et al. 20 showed that a 90 dB white noise would hinder creative thinking compared to the control condition. This is because high white noise levels have been associated with increased distraction, resulting in deteriorated information processing, and thus degraded creativity 23 . In our study, white noise at 65 dB was not too high to impede creativity as suggested by previous studies in related literature. However, our findings show that white noise of 45 dB could support creative thinking in comparison to ambient noise (42.3 dB). This is an important finding as the ambient noise level was relatively equal to the white noise level at 45 dB, which highlights the unique properties of white noise in supporting creativity.
The white noise level at 45 dB allowed for better typing performance in terms of speed and accuracy and led to reduced EDA levels when compared to the white noise at 65 dB. EDA levels have been widely used as indicators of stress in experimental procedures related to environmental interventions 59,60 . Thus, our results support the conclusion that white noise at 45 dB resulted in reduced physiological stress whereas the 65 dB white noise exposure led to increased stress levels while performing cognitively demanding tasks. These findings agree with previous research studies showing that long exposure to high-level white noise results in a stressful response. For example, Liu et al. 61 showed that the exposure to an 80 dB white noise level was enough to induce more stress than a mental arithmetic task. Similarly, Kraus et al. 62 argue that at higher noise intensities, activations of sympathetic nervous activity (bodily response to stressors) are prominent. To that end, we postulate that highstress levels during the 65 dB white noise condition were associated with deteriorated speed and accuracy. This conclusion was further supported by the work of Loewen and Suedfeld 63 who found that masking office noise with a 60 dB white noise led to high arousal and stress as well as reduced task performance among office workers in comparison to a no-noise condition. On the other hand, our 45 dB white noise condition results are unique; www.nature.com/scientificreports/ to the best of our knowledge, there has been no study that investigated the effect of low-level white noise on task performance or stress levels among neurotypical adults. Finally, our results indicate that different tasks might require different white noise levels for optimal performance: at 45 dB white noise level, sustained attention, accuracy, and speed were optimal but working memory improved under the 65 dB white noise level. Research suggests that the necessary dopamine levels for optimal cognitive performance can vary depending on the type of task 9 . For example, memory tasks are usually highly mentally demanding and thus, require higher dopamine levels 64 , which could explain why the 65 dB white noise condition boosted the memory performance of our participants.
While this study contributed to the literature in unique ways as highlighted above, it also holds some limitations. The study did not present enough variability in age and gender to determine the effect of demographics on the relationship between white noise levels and cognitive performance. Also, the study covered two white noise conditions only (45 dB and 65 dB), thus future research directions could perform more studies to uncover the relationship between various white noise levels and cognitive performance, by recruiting more participants as well as examining more white noise levels (e.g., 55 dB and 75 dB) and the personal differences based on gender, age, etc. Moreover, researchers can investigate the effect of different noise colors (e.g., pink, brown, etc.) 65 on the cognitive performance of neurotypical adults, using the same experimental procedure presented in this paper. Additionally, this study did not perform a concurrent analysis of participants' dopamine levels to biologically explain the results at hand. To that end, future research efforts can measure dopamine levels to confirm our conclusions and determine the governing relationship between the dopaminergic circuitry and cognitive performance under various white noise levels. This can be accomplished by measuring the concentration of injected radioligand (radioactive biochemical substance) using a positron emission tomography camera which helps detect the dopamine released in the brain 66 . On the practical side, results from this paper can be used to enhance our understanding of customized workspaces. Hence, future research can investigate the means and methods to integrate the use of white noise as a performance booster in the workplace and customize the exposure to different white noise levels to fit into the requirement of the work task at hand.

Conclusions
This study examined the effect of two white noise conditions, white noise level at 45 dB and white noise level at 65 dB, on the cognitive performance, creativity, and stress levels of neurotypical young adults in a private office space. Our findings showed that white noise level at 45 dB resulted in better cognitive performance in terms of sustained attention, accuracy, and speed of performance as well as enhanced creativity and lower stress levels. On the other hand, the 65 dB white noise condition led to improved working memory but higher stress levels, which leads to the conclusion that different tasks might require different noise levels for optimal performance. These findings are significant, as they extend previous research results about the positive effects white noise has on the cognitive performance of neurotypical adults. Future research directions presented include studying more white noise levels and different noise colors. Similar research might perform a concurrent analysis of participants' dopamine levels to biologically explain the results.

Data availability
The datasets generated and/or analyzed during the current study are not publicly available following the IRB guidelines associated with this study but are available from the corresponding author on reasonable request.